Currency value is relatively stable through actual use as a medium of exchange, salaries paid in the currency, government backing to maintain relatively stable pricing.

Crypto has none of these. And if it's a good investment, then it's definitely not a good currency

>if it's a good investment, then it's definitely not a good currency

The Bank of England would like a word with you.

That's kind of the point. Currencies which are pegged to other currencies at fixed exchange rates aren't good currencies at all. They're subject to sudden catastrophic revaluation. Fortunately most of the major fiat currencies now have floating exchange rates so that's generally no longer a problem.